During the last decade increased attention has been given to the possibility of using bioadhesive/mucoadhesive polymers for drug delivery purposes. It is believed that several problems associated with conventional controlled release drug delivery systems may be reduced or eliminated by using a bioadhesive/mucoadhesive drug delivery system.
In conventional controlled release drug delivery systems no precautions are made in order to localize the delivery system after administration and, furthermore, the contact time in vivo between the drug delivery system and a particular site is often so short that no advantages are to be expected with respect to, e.g., modifying tissue permeability.
Compared with conventional controlled release drug delivery systems, bioadhesive drug delivery systems are believed to be beneficial with respect to the following features:
i) a bioadhesive drug delivery system localizes a drug substance in a particular region, thereby improving and enhancing the bioavailability for drug substances which may have poor bioavailability in themselves, PA0 ii) a bioadhesive drug delivery system leads to a relatively strong interaction between a bioadhesive substance and a mucosa; such an interaction contributes to an increasing contact time between the drug delivery system and the tissue in question and permits localization of the drug delivery system to a specific site, PA0 iii) a bioadhesive drug delivery system is contemplated to prolong delivery of drug substances in almost any non-parenteral route, PA0 iv) a bioadhesive drug delivery system can be localized on a specific site with the purpose of local therapy e.g. treatment of local fungal diseases, permeability modification, protease and other enzyme inhibition, and/or modulation of immunologic expression, PA0 v) a bioadhesive drug delivery system may be targeted to specific diseased tissues, and PA0 vi) a bioadhesive drug delivery system may be employed in those cases where the conventional approach to controlled release drug delivery is unsuitable, i.e. for certain drug substances or classes of drug substances which are not adequately absorbed.
Bioadhesive substances (also denoted mucoadhesive substances) are generally known to be materials that are capable of being bound to a biological membrane and retained on that membrane for an extended period of time. Bioadhesive drug delivery systems have been the subject of a number of patent applications (see e.g. EP-A-0 516 141, WO 93/21906, and EP-A-0 581 581) but to the best of our knowledge only polymers have been regarded as bioadhesive substances. Such polymers include, e.g., acrylic acid homopolymers and copolymers, hydrophilic vinyl polymers, hydrophilic cellulose derivatives, and natural polymers.
In general, bioadhesive compositions are based on a certain content of a bioadhesive substance. As mentioned above known bioadhesive substances are polymeric substances having a molecular weight of above about 10,000. However, use of polymeric substances as bioadhesive substances in e.g. pharmaceutical compositions is limited to certain types of compositions such as, e.g., gels, i.e. compositions having a relatively high dynamic viscosity. Such a limitation is mainly due to the fact that a certain relatively high concentration of the bioadhesive substance has to be present in the composition if the composition in itself is to be bioadhesive. As mentioned above, application of a bioadhesive drug delivery system may be advantageous in many cases where application of conventional drug delivery systems is insufficient with respect to obtaining the desired effect for a predetermined period of time. However, the applicability of known bioadhesive compositions is rather limited as only relatively highly viscous compositions are bioadhesive which leaves out the possibility of e.g. having a bioadhesive sprayable composition or a bioadhesive solution of low dynamic viscosity.